1. Field of the Invention
This invention refers in general to a process for the preparation of .alpha.,.omega.-diamines.
More particularly, this invention refers to a process for the preparation of aliphatic, linear, saturated or unsaturated .alpha.,.omega.-diamines, containing from 8 to 12 carbon atoms, through the reductive amination of the corresponding .alpha.,.omega.-dialdehydes; saturated dialdehydes yielding saturated diamines and unsaturated dialdehydes yielding either unsaturated or saturated diamines.
2. The Prior Art
The industrial importance of both saturated and unsaturated diamines, is known. To cite some of their main uses, they may serve, as primary components or as additives, in the manufacture of the various types of nylon, of fibers, of elastomers, in the formulation of particular types of alkyd resins, and in the preparation of finishing compositions for textile fibers and of adhesives.
The condensation of diamines with dicarboxylic acids of a suitable molecular weight may yield wetting and emulsifying agents useful in particular in the oil industry.
Further the diamines may be used as hardening agents for epoxy resins.
Various methods for the preparation of higher aliphatic .alpha.,.omega.-diamines are known.
The aliphatic .alpha.,.omega.-diamines may for instance be obtained by the reduction of the corresponding dinitriles, which in turn are obtained from oil derivatives through processes having a very high number of stages.
The numerous attempts to simplify such processes have not been successful.
Thus for instance U.S. Pat. No. 2,657,240 discloses a process whereby diamines may be obtained from cycloolefins ozonides. The preparation of hexamethylenediamine by the ozonization of cyclohexene in alcohol followed by a reductive amination treatment of the ozonide formed, is specifically described.
The yield of the diamine thus obtained is however very low (about 30% with respect to the cyclohexane used). H. Schulz and H. Wagner describe in Angewandte Chemie, 62 (1950) pp. 105-118 a method for the preparation of .alpha.,.omega.-diamines starting from the corresponding dialdehydes, by reductive amination in a single stage.
In particular (pp. 111-117) there is described the preparation of 2-oxy-hexamethylenediamine-b .xi.,6 by reductive amination of the corresponding dialdehyde. However this method too is not industrially satisfactory because the yield ot he diamine is only 45-50% and its purity 80-90%.
In view of the importance of the diamine it is obvious that a method affording a higher yield would have great industrial value.